Package org.orekit.propagation

Propagation

This package provides tools to propagate orbital states with different methods.

Propagation is the prediction of the evolution of an initial state. The initial state and the propagated states are represented in OREKIT by a SpacecraftState, which is a simple container for all needed information at a specific date : mass, kinematics, attitude, date, frame. The state provides basic interpolation features allowing to shift it slightly to close dates. For more accurate and farthest dates, several full-featured propagators are available to propagate the state.

Keplerian propagation

The KeplerianPropagator implements the Propagator interface, which ensures that we can obtain a propagated SpacecraftState at any time once the instance is initialized with an initial state. This extrapolation is not a problem with a simple EquinoctialOrbit representation: only the mean anomaly value changes.

Eckstein-Hechler propagation

This analytical model is suited for near circular orbits and inclination neither equatorial nor critical. It considers J2 to J6 potential coefficients correctors, and uses mean parameters to compute the new position. As the Keplerian propagator, it implements the Propagator interface.

TLE propagation

This analytical model allows propagating {org.orekit.propagation.analytical.tle.TLE} data using SGP4 or SDP4 models. It is very easy to initialize, only the initial TLE is needed. As the other analytical propagators, it implements the Propagator interface.

GNSS propagation

These analytical models allow propagating navigation messages such as in GNSS almanacs available thanks to SEM or YUMA files. Each GNSS constellation has its own propagation model availables in org.orekit.propagation.analytical.gnss package.

Numerical propagation

It is the most important part of the OREKIT project. Based on Hipparchus integrators, the NumericalPropagator class realizes the interface between space mechanics and mathematical resolutions. If its utilization seems difficult on first sight, it is in fact quite clear and intuitive.

The mathematical problem to integrate is a 6 dimension time derivative equations system. The six first equations are given by the Gauss equations (expressed in EquinoctialOrbit). This first order system is computed by the TimeDerivativesEquations class. It will be instanced by the propagator and then be modified at each step (a fixed t value) by all the needed force models which will add their contribution, the perturbing acceleration.

The integrators provided by Hipparchus need the state vector at t0, the state vector first time derivate at t0, and then calculates the next step state vector, and ask for the next first time derivative, etc. until it reaches the final asked date.

Semi-analytical propagation

Semi-analytical propagation in Orekit is based on Draper Semi-analytical Satellite Theory (DSST), which is applicable to all orbit types. DSST divides the computation of the osculating orbital elements into two contributions: the mean orbital elements and the short-periodic terms. Both models are developed in the equinoctial orbital elements via the Method of Averaging. Mean orbital elements are computed numerically while short period motion is computed using a combination of analytical and numerical techniques.

Author:

Luc Maisonobe, Fabien Maussion, Pascal Parraud

Interface Summary

Interface	Description
AdditionalDataProvider<T>	This interface allows to modify SpacecraftState and set up additional data.
BoundedPropagator	This interface is intended for ephemerides valid only during a time range.
CartesianToleranceProvider	Interface to define integration tolerances for adaptive schemes (like the embedded Runge-Kutta ones) propagating the position-velocity vector and the mass, for a total of 7 primary dependent variables (in that order).
EphemerisGenerator	Generator for ephemerides.
FieldAdditionalDataProvider<O,T extends CalculusFieldElement<T>>	This interface allows to modify FieldSpacecraftState and set up additional data.
FieldBoundedPropagator<T extends CalculusFieldElement<T>>	This interface is intended for ephemerides valid only during a time range.
FieldEphemerisGenerator<T extends CalculusFieldElement<T>>	Generator for ephemerides.
FieldPropagator<T extends CalculusFieldElement<T>>	This interface provides a way to propagate an orbit at any time.
MatricesHarvester	Interface for extracting State Transition Matrices and Jacobians matrices from spacecraft state.
Propagator	This interface provides a way to propagate an orbit at any time.
ToleranceProvider	Interface to define integration tolerances for adaptive schemes (like the embedded Runge-Kutta ones) propagating the position-velocity vector (or an equivalent set of coordinates) and the mass, for a total of 7 primary dependent variables (in that order).

Class Summary

Class	Description
AbstractMatricesHarvester	Base harvester between two-dimensional Jacobian matrices and one-dimensional additional state arrays.
AbstractPropagator	Common handling of Propagator methods for propagators.
AbstractStateModifier	Abstract base class for modifying state during propagation.
ConstantCartesianToleranceProvider	Class implementing a Cartesian tolerance provider with values independent on input position-velocity vector.
FieldAbstractPropagator<T extends CalculusFieldElement<T>>	Common handling of Propagator methods for analytical propagators.
FieldAbstractStateModifier<T extends CalculusFieldElement<T>>	Abstract base class for modifying state during propagation.
FieldOrbitBlender<T extends CalculusFieldElement<T>>	Orbit blender.
FieldSpacecraftState<T extends CalculusFieldElement<T>>	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
FieldSpacecraftStateInterpolator<KK extends CalculusFieldElement<KK>>	Generic class for spacecraft state interpolator.
OrbitBlender	Orbit blender.
PropagatorsParallelizer	This class provides a way to propagate simultaneously several orbits.
SimpleToleranceProvider	Class implementing a tolerance provider with same relative and absolute tolerances for all dependent variables.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftStateInterpolator	Generic class for spacecraft state interpolator.

Enum Summary

Enum	Description
PropagationType	Enumerate to define the propagation type used by the propagator.